We shall determine ectoenzymes and other membrane markers of peritoneal macrophages (resident and elicited) and activated macrophages from several species. Movement of markers into phagolysosomes during ingestion of various particles will be followed in intact cells and after cell fractionation. Resident peritoneal macrophages are obtained by simple lavage, and elicited macrophages after the intraperitoneal injection of caseinate. Activated macrophages are obtained from animals infected with Listeria, or after in vitro exposure to a lymphokine. Other biochemical and metabolic characteristics of activated macrophages will be checked to determine the nature of "activation". Bactericidal mechanisms in macrophages of various sorts will be defined biochemically and compared with those of polymorphonuclear leukocytes. As a basis for studies with special reference to oxidative mechanisms, we shall extend work on model systems containing peroxide, myeloperoxidase and halide, or peroxide, ascorbate and a divalent transitional metal ion (copper or cobalt). The mechanism of bactericidal action by such systems will be referred to intracellular killing in leukocytes. Biochemical lesions in killed bacteria will be sought at the level of membrane structure, transport, enzyme activity, DNA and proteins. At the cytological level we shall monitor the inward flow of surface markers into phagosomes during ingestion in the various cell types, and in the polymorphonuclear leukocytes particularly we shall attempt to pinpoint the formation of hydrogen peroxide or superoxide. The potential relevance of superoxide formation to bactericidal activity will be investigated with special regard to transport of this species.